It has long been a major challenge to artisans engaged in the formulation of photographic emulsions for lithographic film to find improved emulsion formulations, film articles and/or methods of development that would yield an increasingly sharp reproduction of an image showing superior qualities of contrast. The relatively recent advent of rapid access developers has intensified this challenge to the artisan since some aspects of the chemistry of these newer developers tend to work against the development of high contrast images.
According to the prior art, to obtain high contrast in lithographic films, it necessary to use a high chloride lith emulsion to prepare a film and process the exposed film in a hydroquinone-only developer containing low sulfite. This type of developer had low capacity and was prone to serious degradation of key properties due to aerial oxidation over as little as 1-3 days. The aldehyde bisulfite used to produce the low sulfite concentration also interfered with the hydroquinone using erratic, even non-reproducible development activity. This high contrast "lith effect" (infectious development) was described as early as 1945 in J. Frank. Inst. 239, 221 (1945).
Some initial contrast-enhancing improvements in the art were taught by Trivelli and Smith in U.S. Pat. No. 2,419,975 who noted an increase in speed and contrast by developing in the presence of hydrazine compounds. However, sulfite necessary as an antioxidant in the developer tended to lessen this "hydrazide" effect. Also, many of their hydrazines were used in large quantities and were highly toxic besides being somewhat nonspecific fogging agents that tended to produce high fog in unexposed areas.
Nothnagle, as taught in U.S. Pat. No.4,269,929, improved the hydrazide effect for contrast enhancement by using hydrazines (nucleators) in conjunction with a hydroquinone (H2Q) plus phenidone developer that could contain a high level of sulfite (SO.sub.3.sup.-) to prevent aerial oxidation. By further incorporating an amine compound in the developer, a high capacity, stable, long life developer/film system that gave excellent high contrast and speeds was provided. However, it was found that the amino compound frequently was toxic, volatile, odor producing, azeotrope forming, insoluble in the developer and costly and required a pH of 11.5+. Also, higher pH developers tended to oxidize and deplete more quickly with respect to the H.sub.2 Q contained within them. This leads to contrast, dot quality, speed and pepper problems and inconsistencies. The toxicity of the hydrazides (nucleators) was of minor concern here since they were incorporated into the emulsion.
In Japanese Patent Pub 140340/85, a method to overcome the problems of the amino compound in the developer was described by incorporation of these compounds into the film layer. However, in Japanese Patent Pub 222241/87, problems with incorporating amino ("boosters") compounds were identified that related to their propensity to leach into the developer from the film and cause pepper fog.
Ideally, a high contrast system using a nucleator which works in concert with a booster should have enhanced speeds and gradients with low/no pepper and excellent dot quality, and developable in a non-toxic, non-corrosive stable developer at as low a pH as is practically feasible. Prior art boosters fail many of these goals, are difficult to synthesize, costly and require large concentrations to be effective.
Many of these booster problems are overcome in the prior art by incorporating the booster into the film rather than in the developer. Machonkin, et al., in U.S. Pat. No. 4,975,354, mentions the use of hydrazide compounds, particularly sulfonamide hydrazides with an amino booster that has at least one secondary or tertiary amino group, contains within its structure at least 3 repeating ethyleneoxy units and has a partition coefficient of at least one. However, even these boosters show speed and gradient as well as dot quality variations from sample to sample. These variations are apparent in the examples where the same element compositions are developed under different development conditions. Also, the high molecular weight of some of the compounds requires a large volume of non-aqueous solvent to be included in the emulsion formulation so that the required concentration of booster is soluble in the emulsion. It is not usually desirable to add high volumes of non-aqueous solvent since it can be toxic and can have a deleterious effect on the sensitometric and other properties of the film.
In U.S. Pat. No. 5,139,921 to Takagi, et al., a process is taught for forming super high contrast images using a developer with relatively low pH wherein the film contains a hydrazine and a nucleation accelerator, i.e., booster, that includes alkyl substituted urea and thiourea with a nitro-containing heterocyclic group attached.
Machonkin, et al., in U.S. Pat. No. 4,988,604, teaches a high contrast photographic element that incorporates an aryl sulfonamidophenyl hydrazide containing both thio and ethyleneoxy groups.
It is an object of this invention to provide novel high contrast accelerator or booster compounds for use in conjunction with hydrazide nucleators.
It is a further objective of the invention to provide the foregoing compounds that overcome some of the limitations of the nucleator/booster systems described above.
It is yet a further object to produce improved silver halide (AgX) photographic elements or articles and methods for their manufacture that use these novel boosters incorporated into the film along with hydrazine nucleators.